Re: 9825A Troubleshooting #VintageHPComputers #HP9825


 

If you haven't already, download a copy of the service manual: http://www.hpmuseum.net/document.php?hwfile=1808
Also two sets of schematics are available, one are the hand drawn ones by Tony Duell: http://www.hpmuseum.net/document.php?hwfile=1809
The second are scans of the HP schematics, starting with: http://www.hpmuseum.net/document.php?hwfile=4141
These are easiest to find by searching on www.hpmuseum.net for "9825_schematic".
Then if you can match up the components you are describing with their component names on the schematic, we'll have some common information to help you move forward.

On Mar 2, 2021, at 11:23 AM, Rhys Lowry <rhys.lowry@...> wrote:

I was measuring the 12V rail when it happened and was confused as to why it wasn’t changing the voltage when I turned the pot. As for dead components, the 2N4398 is shorted and it looks like some solder mask was blown off the back. The 2N3055 still tests fine with a 1.2V drop across it. As the now dead diode connected to pins 1 and two of the card, I searched downstream for any damage. I’m sorry to say I did leave it in while I was testing. Lesson learned. I did not see any obvious damage to the main boards (I didn’t have the front section attached). Following both the rails from the blown mask pin and the diode rail was inconclusive. There may be damage I can not see but I can not test it until I get the power supply board up and working again.

The pins I am referencing are the first, second and fourth from the bottom of the picture of the card connector. Blown mask can be seen in the other.
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